1. Field of the Invention:
The invention relates generally to signal receivers and more particularly to a system and a method for a satellite receiver to receive a downlink signal from a satellite and to receive a control message from a source other than the downlink signal.
2. Description of the Prior Art:
A geostationary satellite system is commonly used to send a program of audio/video or data from one sending location to many receiving locations. An important benefit of the satellite system is the ability to send the program to remote locations that are not wired to telephone lines. The satellite system includes a system manager on Earth to select the program, a satellite in space to receive the program in an uplink signal and to re-transmit the program in a downlink signal to one or more signal receivers on Earth. Many system managers simultaneously send multiple programs using many satellites. The signal receiver includes an antenna to select the satellite transmitting the desired program by positioning the antenna in a desired elevation and azimuth relative to the desired satellite. In order to allow the signal receiver to further distinguish the desired program, the downlink signals are divided into channels by frequency, time, polarization and modulation. The signal receiver selects the channel of the downlink signal having the desired program.
One application of the satellite system is "distant learning". In distant learning a live or recorded audio/video program is sent from the system manager simultaneously to many signal receivers with each receiver being located in a classroom. Such classrooms may be distinctly located in various different locations. Conceptual proposals having as many as 2,000 classrooms in a system have been made. A problem in distant learning and use of existing satellite systems is that the signal receiver may become tuned to a channel other than the channel used for the distant learning event. This occurs because multiple satellites having multiple downlink signal channels are used in the application or because the receiver is used to receive other programs during time periods used for the distant learning application. Satellite and channel changing is a common occurrence in signal receivers in classrooms due to multiple uses of the receiver during evenings and weekends by teachers and coaches for various other purposes. The channel used in the application cannot be used to carry message information to re-tune the receiver because the receiver is not receiving that channel. Typically, an experienced operator is then required to re-tune the receiver to the correct satellite and channel for the distance learning program. One method of eliminating the requirement of the experienced operator is by controlling the signal receiver with a message sent over the telephone system to a telephone modem that is located with the receiver. However, a limitation of the use of the telephone system to control multiple sites and to send the message to all sites is that many telephone calls may need to be made approximately simultaneously to send the message to all sites. A further limitation is that a telephone line must be installed adjacent to the signal receiver. The requirement for the telephone line may eliminate the benefit of the satellite system of being capable of sending information to a remote location. Further, some sites, such as the classrooms in some school districts, impose a level of bureaucracy that makes the installation of a telephone line impractical.
There is a need for a signal receiver capable of receiving a plurality of satellite downlink channels carrying programs for audio/video or data and of receiving an airwave message signal, from a source other than the received channel, to properly prepare the receiver for selecting the correct satellite downlink channel having the desired program. There is a further need for a wireless control system to broadcast the airwave message signal to many signal receivers simultaneously.